The research proposed in this application is designed to examine individual differences in electrophysiological measures of anterior activation asymmetry and their relation to variations in mood and affective reactivity. The research is designed to replicate and extend recent findings from our laboratory which indicate that anterior activation asymmetries are stable over time and predict mood and affective reactivity. Anterior asymmetry is viewed as a diathesis, which in combination with the requisite environmental elicitor, will bias emotional reactivity. Right anterior activation during baseline predicts greater negative affect in response to an appropriate elicitor, while left anterior activation predicts the reverse. These basic findings will be extended in two large studies. In each study, an independent cohort of 156 subjects will be assessed on baseline measures of anterior asymmetry on three occasions. Relations between anterior asymmetry across the three sessions and reactivity to positive and negative emotional film clips, cold pressor pain and a cognitive task constructed to produce failure will be evaluated across the two studies. In addition, relations between individual differences in anterior asymmetry and measures of cellular immune function will be studied to confirm and extend our initial findings which indicate decreased natural killer cell activity in subjects with extreme right frontal activation compared to subjects showing extreme left frontal activation. Relations between individual differences in anterior asymmetry and startle magnitude will also be assessed to examine the hypothesis that subjects with greater right anterior activation will show accentuated startle magnitude compared with their left anterior activated counterparts.